1. Field of the Invention
The present invention relates to a development apparatus for developing latent electrostatic images to visible toner images, and more particularly to a development apparatus including a development roller with a surface layer comprising a trifluoropropyl-group-containing fluorosilicone polymer.
2. Discussion of the Background
Conventionally, there is known a method of developing latent electrostatic images by a non-magnetic one-component toner, in which method the toner is supplied onto a development roller and formed into a thin layer by a toner layer thickness regulation means such as a blade-shaped member or roller-shaped member, and the thus formed toner layer is then brought into contact with a latent electrostatic image formed on an electrophotographic photoconductor, whereby the latent electrostatic image is developed to a visible toner image.
In the aforementioned development method, it is generally necessary that the development roller meet the following requirements:
(1) The surface layer of the development roller has such a low hardness that a sufficiently large contact area can be obtained between the development roller and the photoconductor. For instance, it is made of a material with a degree of hardness ranging from 30 to 40 in accordance with JIS K 6301 (JIS A).
(2) The material for the surface layer of the development roller has appropriate electric properties to achieve excellent development performance. In the case where the surface layer is made of a rubber, with a thickness of several millimeters, the rubber layer has a volume resistivity of 10.sup.8 to 10.sup.12 .OMEGA..cm.
(3) The aforementioned hardness and electric properties do not change depending upon the environmental conditions, in particular, by the ambient temperature and humidity.
Conventionally, nitril-butadiene rubber (NBR), epichlorohydrin rubber (ECO), urethane rubber, acrylic rubber and chloroprene rubber are used as the materials for the surface layer of the development roller. These conventional rubber materials can satisfy the above-mentioned requirements (1) and (2), but do not satisfy the requirement (3). In particular, the electric properties considerably vary depending on the changes in temperature and humidity.